Promark - formally "Gorilla" doesn't get such great reviews for one thing....the other is you have to add all the same components to actually compare them.
Their 4500 winch comes in at $180 ....then add all the same items the Viper comes with; synthetic rope, hawse fairlead, snatch block, remote (they only give you one in their kit) , mounting hardware and your total is $362.
The Viper comes complete at $356 and change.
Besides, I don't want to mess with adding all the extra stuff - especially spooling out wire and adding synthetic - when I can buy a complete kit that goes in right the first time.
Viper 4500 lb winch, $236 shipped from Amazon.com and thats w/the RZR mounting kit. I didnt go synthetic (I already had a synthetic rope kit at my house) but it would only be another $30 bucks or so from them